Time-resolved studies of photoinitiated reactions in binary and larger (N2O) m (HI) n (m? 1, n? 1) complexes

Under gas-phase conditions, reaction of fast hydrogen atoms with N2O lead mainly to OH(X2Π)+ N2(X1∑) products via a 1,3 hydrogen-shift mechanism involving the HNNO intermediate. In complexes formed by using supersonic expansions, the reaction mechanism is less clear. In this paper, OH build-up times are reported for photoinitiated reactions in complexes of the form (N2O)m(HI)n with m 1 and n 1. The build-up times vary from many hundreds of fs under conditions that encourage the formation of larger complexes (i.e. the highest stagnation pressures) down to ⩽ 100 fs for the lowest stagnation pressures. We conclude that in binary complexes OH is produced on timescales below 100 fs. This rules out the participation of a long-lived intermediate such as HNNO. Comparisons are made with the analogous CO2–HI system, in which reactions in larger complexes either yield the same lifetimes as do binary complexes or are inhibited, presumably because of the relatively large H + CO2 entrance channel barrier.